Is there a window of opportunity for microbial colonization in the root microbiota?

Background/Question/Methods

While we are learning more about the importance of microbial communities for plant health and productivity, it remains unresolved how these communities change over time and to what degree we are able to manipulate their composition. Is it possible that there is a window of opportunity for microbes to colonize a root system? We know that plants are exposed to different microbes throughout their lives and that many seeds and seedlings used for commercial purposes are sterilized before planting. But how do these differences affect the developing plant microbiota? In our study, we tested the effect of inoculation timing on microbial community composition in roots of Setaria viridis. We hypothesized that plants exposed to the same microbial inoculum at different developmental stages would form distinct root microbiota based on the idea that plants could be more or less receptive to colonization at different developmental stages. We grew plants under sterile conditions and introduced them to a community of soil microbes at different ages representing various developmental stages. Half of the plants were harvested 2 weeks after inoculation and the remaining plants were harvested once they reached the age of 12 weeks. Root bacterial communities were determined using 454 sequencing. 

Results/Conclusions

We found that the age at which a plant was introduced to soil microbes had little effect on the ultimate community composition of the bacterial root microbiota. Results showed that the amount of time the community had to establish after inoculation was important as well as the age of the plant. In general, although plants inoculated at different ages showed significant differences in communities early on (at the 2 week harvest), these were less apparent by the end of the experiment when all plants had reached the same age. In conclusion, timing of inoculation seems to have a greater impact over short terms than in the long run, but further examination of community stability at various developmental stages would be useful to better understand how prone microbial root communities are to change.